One of the rarest of all facetable gems, cut cuprites can show magnificent deep red color. However, these beautiful stones are too fragile for most jewelry uses.
Cuprite
Value
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Poorly cut cuprites will appear very dark and dull. Quality cutting will bring out their striking red colors and near-metallic luster, boosting their value.
You’re more likely to find cuprites in mineral collections than jewelry collections. With a hardness of just 3.5 to 4, they scratch easily. Thus, these gems aren’t very suitable for use as ring stones. Pendants, earrings, and brooches are less risky options. Nevertheless, use protective settings for any cuprite jewelry pieces.
Cuprite crystals are typically too small and opaque for faceting. However, cuprite often occurs mixed with other copper-bearing minerals, such as malachite, chrysocolla, and azurite. Lapidaries can carve these mixed stones into cabochons.
Cuprite’s very high refractive index (RI) of 2.848 and specific gravity (SG) of 6-6.14 will usually easily help distinguish cuprites from gemstones with similar color and appearance, especially more popular red gemstones like garnets, rubies, and spinels. However, other rare red gemstones of similar appearance — such as proustites, rutiles, and wulfenites — also have over-the-limit (OTL) RIs that overlap or approximate cuprite’s. SG measurements should still distinguish these gems.
Cuprites have a brownish red streak. Please note that streak testing is destructive and should only be conducted as a last resort for identification and never on a finished gem.
As isometric crystals, cuprites have no birefringence or pleochroism, but some stones may show these properties anomalously. Polishing faceted cuprites with diamond paste may leave surface deformations that cause anomalous birefringence. One study has found that polishing with alkaline silica solutions instead can avoid this result.
Are There Synthetic Cuprites?
Scientists have synthesized cuprites for many purposes, including research into anti-fouling paints, the removal of patinas from bronze archeological finds, and other chemical and mineralogical processes. Crystals have also been synthesized, some have even been faceted. However, there doesn’t appear to be widespread use of this lab-created material for jewelry.
As a mineral, cuprite occurs in many locations worldwide. However, to date, only one locality — Onganja, Namibia — has produced blood red crystals transparent and large enough to facet. (Most material from this mine is still opaque and often coated with a layer of malachite). Now closed and flooded, this mine probably won’t produce any more cuprite. Since mineral collectors prize these fine crystals and don’t want to see them cut, the availability of facetable material in the marketplace is very limited.
Before the amazing Onganja discovery in 1973, the largest known cuprites weighed less than one carat. Onganja cuprites may reach sizes of 6″ across or more, and lapidaries have cut flawless stones up to 300 carats. Even larger finished stones may be possible.
Wearing or handling finished cuprites should pose no hazards. However, gem cutters should take precautions when working with this material. Due to its copper content, cuprite dust is toxic. Accidental ingestion could lead to acute distress, like vomiting, and chronic exposure could lead to liver and kidney damage. Lapidaries should wear protective masks and, ideally, use a glovebox to prevent inhaling or ingesting cuprite particles during cutting, polishing, and cleaning.
Caring for Cuprites
Over time, cuprites will lose their color from exposure to light. Store them away from light sources and reserve any jewelry for occasional evening wear.
Clean these gems only with water, mild detergent, and a soft brush. Consult our gemstone jewelry cleaning guide for more care recommendations.